1. Field of the Invention
The present invention relates to a constant pressure preload linear guide bearing apparatus in which the wear and vibration of rolling members are reduced by applying a constant pressure preload to the rolling members which are interposed between a guide rail and a slider.
2. Description of the Prior Art
Prior art linear guide bearing apparatus are, for example, shown in FIGS. 10 to 12. In either case, a slider 2 is straddlingly mounted on a guide rail 1 through a plurality of balls 3 as rolling members. The slider 2 moves very smoothly on the guide rail 1 with a small force owing to a circular rolling motion of the balls 3. During the movement of the slider 2, in order to maintain a high motion accuracy by suppressing pitching and yawing of the slider 2 and in order to increase the rigidity by reducing the amount of elastic deformation due to an external load, typically, the linear guide bearing is applied with a preload.
Various types of preloading are available. FIGS. 10 and 11 show one type in which the balls 3 which are interposed between the guide rail 1 and the slider 2 are made as over-sized balls and are fitted with an interference between the guide rail 1 and the slider 2. Specifically, the steel balls 3 which are slightly larger than a ball space formed between a ball groove 4 of the guide rail 1 and a ball groove 5 of the slider 2, both of the grooves 4 and 5 being opposing each other, are inserted into a ball space to thereby apply a fixed position preload. On the other hand, FIG. 12 shows another type of preloading in which a bearing plate 6 carrying a ball groove 5 of a slider 2 is pressed towards a guide rail by clamping a preload adjusting screw 7 thereto to apply a fixed position preload.
However, in the prior art preloading mechanisms described above, each applies a fixed position preload. Such a fixed position preload involves a problem in that the preload is reduced due to initial wear, or wear which increases progressively during use and, when the wear is further increased, a gap will be formed between a ball groove surface and the balls.
Furthermore, in a linear guide bearing apparatus using rolling members, such as steel balls or rollers, a problem is involved in that although frictional resistance is small and movement is smooth as compared with slide guide apparatus, the damping effect for vibrations is very inferior.